Process for forming a furnace wall

ABSTRACT

A monolithic refractory composition, which can be rapidly dried after being mixed with water and applied to a desired portion by casting or spraying to form a furnace wall, and which comprises refractory aggregates, a refractory powder, an aluminum alloy powder and a dispersant, wherein the aluminum alloy powder is contained in an amount of from 0.04 to 5 parts by weight per 100 parts by weight of the total amount of the refractory aggregates and the refractory powder.

This application is a division of application Ser. No. 08/671,546, filedon Jun. 27, 1996 now U.S. Pat. No. 5,783,510.

The present invention relates to a monolithic refractory composition forrefractories which are useful as lining materials for various furnaces,lining materials for refining containers such as ladles or liningmaterials for refining lances or troughs, which are free from explosionduring heat drying, and a process for forming a furnace wall by means ofsuch a composition.

Monolithic refractories have been widely employed in recent years, sincethe man power required for their application is little, they can beapplied in optional shapes, and the properties of refractories have beenimproved. Especially, cast refractories are presently most commonly usedas monolithic refractories, since their applicability is excellent, andthe unit cost and unit material can now be remarkably reduced owing toan improvement in the technology for densification to improve the usefullife and owing to reworkability of used material.

With respect to cast refractories, various bonding methods have beenpractically employed owing to recent developments in materials andapplication techniques, and it has been made possible to obtain a lininghaving a dense structure by a combination with various ultrafinepowders, dispersants or flocculants. However, such a dense castrefractory lining has a problem that when it is heated for drying toquickly remove water mixed for application, steam is likely to betrapped in the interior of the lining during the temperature rise, andthe lining is likely to crack or break due to the steam pressure(hereinafter referred to as explosion or a explosion phenomenon).Therefore, drying of a cast dense refractory is carried out slowly overa long period of time, and it takes a correspondingly long workingperiod for the application. To shorten the working period by preventingthe explosion phenomenon, a technique to prevent explosion has beenproposed in which an aluminum powder (hereinafter referred to as Alpowder) is added to cast refractories, so that H₂ gas is generated bythe reaction of Ca+ contained in aluminous cement with an aqueousalkaline solution, to form gas permeable pores through which steam maybe released (e.g. Japanese Examined Patent Publication No. 38154/1986).

However, if Al powder is added, the lining is likely to expand to form aporous body due to the pressure of H₂ gas generated. Further, due to thepressure of H₂ gas, cracking is likely to form in the internal structureof the refractories, and the composition for cast refractories having Alpowder added thereto, lacks in storage stability, since the activity ofAl powder is high. Furthermore, with cast refractories having Al powderadded thereto, it has been difficult to obtain a lining of refractorieshaving constant quality, due to the influence of the exothermic reactionwhich is variable depending upon the application temperature or the typeof the aluminous cement to be incorporated.

Al powder is highly active so that the reaction proceeds too quickly.Accordingly, it has been proposed to control the reaction by coating thesurface of Al powder particles with e.g. an organic substance (e.g.Japanese Unexamined Patent Publication No. 120573/1983). Further, whenAl powder is used for the purpose of preventing explosion, hydrogenthereby generated is inflammable, and if the application is carried outin a closed space, an explosion is likely to occur. Accordingly, a duecare will be required.

The method of coating the surface of Al powder particles with an organicsubstance, proposed as a method for solving such problems, is effectivefor improving the storage stability, but it is still difficult tocontrol the timing for generating H₂ gas, and it is difficult touniformly distribute H₂ gas bubbles throughout the castable material,whereby large bubbles are likely to be formed locally to deteriorate theuseful life of refractories.

Recently, as a safer explosion-preventing technique than Al powder, amethod of forming gas permeable pores by adding organic or inorganicfibers to the composition, has been proposed (e.g. Japanese UnexaminedPatent Publication No. 190276/1984). Further, Japanese Unexamined PatentPublication No. 100483/1987 proposes a method for preventing explosion,which comprises incorporating a basic aluminum lactate in addition to Alpowder, to form fine cracks in the refractory structure thereby to formgas permeable pores.

However, the method of adding organic fibers, proposed as a safe methodfree from explosion due to inflammation of H₂ gas generated, hasdrawbacks such that the dispersibility of organic fibers in the batch ispoor, the a mount of the organic fibers to be incorporated is limited,for example, for a reason that the amount of water required at the timeof the application increases and the useful life of the refractoriestends to be impaired, and it is thus difficult to obtain an excellentrefractory lining.

Further, the method of adding a basic aluminum lactate, has a problemthat since the shrinkage during drying is substantial, laminar crackingis likely to occur in the lining, whereby the useful life of therefractories will be impaired.

Further, it has been proposed to add an aluminum-silicon alloy powder tomonolithic refractories (Japanese Unexamined Patent Publication No.217472/1983). However, here, the aluminum-silicon alloy powder is usedfor the purposes of strengthening a joint portion of the appliedrefractories and improving the resistance against mechanical andchemical wearing off at a high temperature, and there is no suggestionfor solving the problems which occur during the heating and drying theapplied monolithic refractories.

On the other hand, spray application of refractories requires no formsas opposed to cast refractories and thus has a merit that the man powercan be remarkably saved in the application operation. Accordingly, sprayapplication of refractories has already been practically employed insome areas. Such conventional spray refractories include, for example,the one containing aluminous cement, the one having a hardeningaccelerator such as a lithium salt or sodium aluminate incorporatedthereto, the one having a hardening agent such as sodium silicofluorideor condensed aluminum phosphate combined to water glass, and the onehaving aluminum phosphate or various alkali metal phosphates combined towater glass.

However, conventional application methods are so-called dry or semi-wetspray application methods, as disclosed in Japanese Examined PatentPublication No. 27308/1990 and Japanese Unexamined Patent PublicationNo. 36071/1987. Namely, a batch composed of a dry composition or a wetcomposition having water mixed in such an amount not to impartflowability, is transported to a spray nozzle at the application fieldby a piping by means of compressed air as a carrier, and sprayapplication of refractories is carried out by the spray nozzle whileinjecting whole necessary water or supplemental amount of water requiredby the batch and a rapid setting agent at the spray nozzle or before thespray nozzle.

However, by such a method, fine particles of e.g. less than 0.1 mm inthe composition, tend to be applied by spraying in an inadequatelydispersed or wetted state, and a large amount of air tends to beincluded in the applied batch of refractories. As a result, theresulting refractories will have a high porosity as compared withrefractories formed by casting. As the porosity is high, they tend to beinferior in the refractory properties such as corrosion resistance.Further, there has been a working environmental problem such that dustis scattered during application, and the application yield has been poorwith a substantial amount of rebound loss.

On the other hand, it has been attempted to produce a dense lininghaving a low porosity by improving the spray nozzle or the spraytechnique (apparatus).

However, it has been found that since the spray-applied lining ofrefractories has a high density, water in the lining is trapped in thelining in the state of steam during the drying operation or use, and ifthe lining is rapidly heated, the explosion is likely to result due toan increase of the steam pressure.

It is an object of the present invention to provide a cast or sprayrefractory composition which is capable of solving the above problemsand which is capable of forming a furnace wall of a dense monolithicrefractory without a danger of explosion even when subjected to rapidheating and drying.

In a first aspect, the present invention provides a monolithicrefractory composition, which can be rapidly dried after mixed withwater and applied to a desired portion by casting or spraying to form afurnace wall, and which comprises refractory aggregates, a refractorypowder, an aluminum alloy powder and a dispersant, wherein the aluminumalloy powder is contained in an amount of from 0.04 to 5 parts by weightper 100 parts by weight of the total amount of the refractory aggregatesand the refractory powder.

In a second aspect, the present invention provides a self flowable batchprepared by mixing, together with at most 12 parts by weight of water,100 parts by weight of a monolithic refractory composition comprisingrefractory aggregates, a refractory powder, an aluminum alloy powder anda dispersant, wherein the aluminum alloy powder is contained in anamount of from 0.05 to 3 parts by weight per 100 parts by weight of thetotal amount of the refractory aggregates and the refractory powder,said self flowable batch having a flowability such that when the batchimmediately after the mixing is fed to fill a truncated cone mold havingopen upper and lower ends and having an upper end inner diameter of 50mm, a lower end inner diameter of 100 mm and a height of 150 mm, thenthe truncated cone mold is withdrawn upward, and the batch is left tostand still for 60 seconds, the mean spread diameter of the batch is atleast 190 mm.

In a third aspect, the present invention provides a process for forminga furnace wall, which comprises applying to a predetermined furnacewall-forming portion by casting or spraying, a monolithic refractorybatch prepared by mixing a predetermined amount of water to acomposition comprising refractory aggregates, a refractory powder, adispersant and an aluminum alloy powder, wherein the aluminum alloypowder is contained in an amount of from 0.04 to 5, preferably from 0.04to 3 parts by weight per 100 parts by weight of the total amount of therefractory aggregates and the refractory powder, then heating arefractory thus applied at a temperature rising rate of from 50 to 400°C./hr at the surface of the refractory, wherein the heat treatment iscarried out at least until the temperature of the surface of therefractory becomes at least 500° C., to dry the refractory.

Now, the present invention will be described in detail with reference tothe preferred embodiments.

Firstly, a monolithic refractory composition for casting (which may bereferred to simply as a cast refractory composition) and a process forforming a furnace wall employing it, will be described, in which themonolithic refractory composition of the present invention is applied bycasting to a portion desired to have the furnace wall formed.

The cast refractory composition of the present invention comprisingrefractory aggregates, a refractory powder, an Al alloy powder and adispersant, is mixed by an addition of water at the time of applicationand then applied by a casting application method. The refractoryaggregates are the main constituting component of refractories, and therefractory powder is a component which fills spaces of the refractoryaggregates and constitutes a matrix for binding the refractoryaggregates. The dispersant is added to increase the flowability of abatch which is prepared by mixing the composition with water.

As the refractory aggregates, at least one type of aggregates selectedfrom the group consisting of alumina, bauxite, diaspore, mullite,aluminous shale, shamotte, silica rock, pyrophillite, sillimanite,andalusite, spinel, magnesia, silicon carbide and graphite is preferablyemployed.

The refractory powder is preferably at least one member selected fromthe group consisting of aluminous cement, refractory clay, refractoryaggregate powder, fumed silica and ultrafine powder alumina.

The refractory powder is preferably a powder having an average particlesize of at most 30 μm, so that it is capable of forming a good matrix.Further, it is preferred to incorporate, as a part of such a refractorypowder, an ultrafine powder of e.g. alumina or fumed silica having anaverage particle size of at most 3 μm, preferably at most 1 μm, wherebyit is possible to reduce the amount of water to be added to thecomposition, and it is possible to impart good flowability to the batchi.g. the composition mixed with water.

Further, when aluminous cement is used as a part of the refractorypowder, the aluminous cement serves to bond the cast refractories, andit is thereby possible to impart practical strength to the resultinglining within a wide temperature range of from room temperature to ahigh temperature. Such aluminous cement is preferably incorporated in anamount of from 1 to 10 parts by weight per 100 parts by weight of thetotal amount of the refractory aggregates and the refractory powder. Thealuminous cement preferably has a CaO/Al₂ O₃ molar ratio of at most 1.3,whereby a sufficiently long useful time can be secured for the mixedbatch. Further, when refractory clay is used as a part of the refractorypowder, it is possible to obtain a cast refractory composition excellentin the applicability with clay bonding.

In the present invention, the blend proportions of the refractoryaggregates and the refractory powder are usually preferably such thatthe refractory aggregates are from 75 to 95 wt %, and the refractorypowder is from 5 to 25 wt %.

Further, in order to impart excellent flowability to the mixed batch, itis preferred to incorporate to the composition a dispersant properlyselected depending upon the types of the refractory aggregates and therefractory powder used. Further, if a powdery dispersant is used, it ispossible to preliminarily add the dispersant to the composition to bepackaged in a bag. The dispersant is preferably at least one memberselected from the group consisting of poly-phosphate salts,poly-carboxylate salts, poly-acrylate salts and β-naphtalensulfonatesalts. The dispersant is preferably incorporated in an amount of from0.02 to 1 part by weight per 100 parts by weight of the total amount ofthe refractory aggregates and the refractory powder in the composition.

With the cast refractories having aluminous cement incorporated, thehardening time varies depending upon the application temperature or thetype of the aluminous cement. For example, there may be a case wherehardening is slow at a temperature of not higher than 15° C., a casewhere hardening is slow at a temperature around 30° C., or a case wherehardening proceeds quickly when the temperature exceeds 30° C. Tocontrol the hardening time so that application can be carried outwithout being influenced by the surrounding temperature condition, it ispreferred to incorporate a hardening accelerator or a hardeningretarder.

As the hardening accelerator, quicklime, lithium carbonate or calciumchloride may preferably be employed. As the hardening retarder, anitrate, a phosphate, a lignin sulfonate or a gluconate may preferablybe employed. Such a hardening accelerator or retarder may beincorporated in an amount within a range of from 0.01 to 1 part byweight per 100 parts by weight of the total amount of the refractoryaggregates and the refractory powder, and the amount is preferablyadjusted depending upon the application temperature or the type ofaluminous cement.

The Al alloy powder to be incorporated to the composition may be any Alalloy powder. However, an aluminum-silicon (Al--Si) alloy powder or analuminum-magnesium (Al--Mg) alloy powder is preferred. Most preferredfrom the practical view point is an Al--Si alloy powder. It is alsopossible to use a combination of the Al--Si alloy powder and the Al--Mgalloy powder. Further, a small amount of a metal powder other than thealuminum powder may be mixed to the Al--Si alloy powder or the Al--Mgalloy powder to such an extent not to impair the effects intended by thepresent invention.

In the present invention, with the composition having the Al alloypowder incorporated, it is possible to adjust the amount and the timingfor generation of H₂ gas. This is attributable to the fact that the Sior Mg component contained in the Al alloy controls the reactivity of theAl component to control generation of H₂ gas. Thus, generation of H₂ gasis less influenced by the application temperature or the type ofaluminum cement, as compared with the case where Al powder isincorporated, and the reaction for generation of H₂ gas takes placemildly, whereby gas permeable pores suitable for discharging steam cancertainly be formed.

By the presence of formed gas permeable pores, explosion can be avoidedeven when the lining of cast refractories is rapidly heated at the timeof drying. Further, it is readily possible to avoid a danger ofinflammation explosion due to generation of H₂ gas, as no rapidgeneration of H₂ gas will occur as opposed to refractories having Alpowder incorporated. Further, the Al--Si or Mg alloy powder is lessreactive with moisture in air than Al powder. Accordingly, the castrefractory composition packaged in a bag has good storage stability.

Further, the Al--Si alloy powder changes finally to Al₂ O₃ and SiO₂ i.e.refractory components. Thus, it is excellent in the properties requiredfor refractories, and the volume increases when the Al--Si alloy powderchanges to a Al₂ O₃ and SiO₂, whereby it is possible to obtain a castrefractory furnace wall excellent in the volume stability. Further, inthe lining made of the cast refractory composition of the presentinvention, the Al--Si alloy powder will be oxidized to form Al₂ O₃ andSiO₂ which contribute to the bond strength, whereby it is possible toobtain a refractory furnace wall excellent also in the strength.

Likewise, the Al--Mg alloy powder will finally be converted torefractory components such as Al₂ O₃, MgO and MgAl₂ O₄. Thus, it ispossible to obtain cast refractories which are excellent in theproperties as refractories and which are excellent in the volumestability as the volume increases when the Al--Mg alloy powder changesinto Al₂ O₃, MgO and MgAl₂ O₄. Further, with the lining made of the castrefractory composition of the present invention, the Al--Mg alloy powderwill be oxidized to form Al₂ O₃ and MgO which contribute to theimprovement of bond strength, whereby it is possible to obtainrefractories excellent also in strength.

The amount of the Al--Si or Mg alloy powder to be added to thecomposition, is usually from 0.04 to 5, preferably from 0.04 to 3 partsby weight, per 100 parts by weight of the total amount of the refractoryaggregates and the refractory powder in the composition. If the amountis less than 0.04 part by weight, generation of H₂ gas tends to besmall, whereby it tends to be difficult to obtain the effect forpreventing explosion. On the other hand, if it exceeds 5 parts byweight, the amount of H₂ gas generated tends to be large, wherebybulging or cracking tends to be observed in the refractories afterapplication, and if gas bubbles are generated so much that a porous bodywill be formed, the strength of the refractory tends to be low.Preferably, the amount of the Al--Si or Mg alloy powder is from 0.04 to3, more preferably from 0.1 to 2.0 parts by weight.

The Al--Si or Mg alloy powder incorporated in the cast refractorycomposition of the present invention is preferably the one whichcomprises from 60 to 95 wt % of Al and from 5 to 40 wt % of Si or Mg. Ifthe Si or Mg component in the Al--Si or Mg alloy exceeds 40 wt %,generation of H₂ gas tends to be slow, and the amount of the generatedgas tends to be small, whereby the effects for preventing explosion,tend to be small. On the other hand, if the Si or Mg component is lessthan 5 wt %, generation of H₂ becomes active, and depending upon thecomponents to be incorporated to the composition, bulging or crackingtends to occur in the lining of refractories. More preferably, theAl--Si or Mg alloy powder comprises from 85 to 93 wt % of Al and from 7to 15 wt % of Si or Mg.

The Al--Si or Mg alloy powder incorporated in the cast refractorycomposition of the present invention, is preferably the one wherein thetotal amount of the Al component and the Si or Mg component is at least90 wt %, and particles having a particle size of at most 0.074 mm arecontained in an amount of at least 40 wt %.

When the total amount of Al and Si or Mg is at least 90 wt %, it ispossible to obtain a desired effect such that a fluctuation in theinitiation time of the reaction can be minimized. The total amount of Aland Si or Mg in the Al--Si or Mg alloy is more preferably at least 95 wt%. Further, when the Al--Si or Mg alloy powder contains at least 40 wt %of particles having a particle size of at most 0.074 mm, it is possibleto obtain an effect for certainly preventing explosion. If the particleshaving a particle size of at most 0.074 mm, are less than 40 wt %,generation of H₂ gas tends to be small, whereby the effect forpreventing explosion tends to be small. More preferably, the Al--Si orMg alloy powder contains at least 50 wt % of particles having a particlesize of at most 0.074 mm.

The Al--Si or Mg alloy powder is preferably an alloy powder wherein theAl component and the Si or Mg components are uniformly dispersed. Suchan alloy powder can be prepared by an atomizing method or a method ofpulverizing a melt-solidified product of the alloy.

The amount of water to be mixed to the composition varies depending uponthe porosity and the specific gravities of the refractory aggregates andthe refractory powder contained in the composition. The amount of watercapable of imparting flowability to the batch has a lower limit. Namely,water is usually required to be in an amount of at least 4 parts byweight per 100 parts by weight of the total amount of the refractoryaggregates and the refractory powder. In order to minimize the porosityof the refractories after application and to secure excellent physicalproperties as refractories, the amount of water to be mixed to thecomposition is preferably at most 12 parts by weight, more preferably atmost 10 parts by weight, per 100 parts by weight of the total amount ofthe refractory aggregates and the refractory powder. If the amount ofwater to be mixed to the composition is large, the refractory aggregatestend to sediment, whereby the applied refractories tend to benon-uniform.

The cast refractory composition of the present invention is used in sucha manner that water is mixed to the composition having theabove-described blend proportions, to impart flowability, and theobtained batch is applied to a portion desired to have a furnace wallformed, by casting (in a case of a composition having no adequate selfflowability such as the one wherein the refractory powder is composedsolely of aluminous cement or the one having clay added thereto, theapplication is carried out under vibration), and no explosion phenomenontakes place even when the resulting monolithic refractory after curingthe applied lining, is dried at a rapid heating up rate of from 50 to400° C./hr at the surface of the refractory to the maximum temperatureof 1400° C.

If the heating up rate is less than 50° C./hr, the superiority over theconventional drying method is not sufficient, and the drying time maynot substantially be shortened. On the other hand, if it exceeds 400°C./hr, a correspondingly large sized drying means will be required, andeven if the temperature is raised so quickly, heat accumulation to thefurnace wall will be inadequate, and it takes time for complete removalof water. Further, if the temperature rising rate exceeds 400° C./hr,spalling cracks are likely to form on the surface of the monolithicrefractory.

The heating up rate can be optionally determined depending upon theblend proportions of the composition, the shape and the thickness of thefurnace wall to be formed and operational conditions to which thefurnace wall is exposed. In most cases, a heating up rate of at least100° C./hr is sufficient, and in some cases the heating up rate may beat least 300° C./hr.

The maximum temperature for heating is at a level of 500° C. dependingupon the furnace, to form a practically useful furnace wall. However,usually, a desired furnace wall is formed by heating to a maximumtemperature of at least 1500° C.

According to the present invention, heating and drying can be carriedout at such a rapid heating up rate in a short period of time, whichmakes quick reoperation of the furnace possible.

In the present invention, the surface temperature for heating fordrying, is a temperature measured at a position of from 1 to 2 mm fromthe surface of the refractory formed as a furnace wall, by a thermometer(usually a thermocouple) embedded in the refractory so that the forwardend is located at said position.

In the present invention, the heating up rate is influenced also by thethickness of the monolithic refractory formed. For example, as thethickness increases, a longer period of time is required for drying tothe interior.

However, the thickness of the monolithic refractory of the presentinvention is usually within a range of from 100 to 1,000 mm.Accordingly, when the refractory is heated for drying at a prescribedheating up rate until the surface temperature becomes at least 500° C.,the furnace wall can be formed without bringing out explosion orcracking during the heating up and drying operation. Even if a non-driedportion partially remains in the interior, there will be no problemsince such portion will be gradually dried during practical use of thefurnace.

The monolithic refractory composition of the present invention isusually applied on an inner surface of a furnace comprising a permanentrefractory and an heat insulating refractory formed sequentially fromthe rear side of the furnace.

Now, a monolithic refractory composition for spraying (which may bereferred also as a spray refractory composition) will be described,whereby a furnace wall is formed by spraying.

For the process for forming a furnace wall by means of the sprayrefractory composition of the present invention, the same heating anddrying conditions, i.e. the same heating and drying conditions by rapidheating up, as used for the cast refractory composition, may be applied.

The spray refractory composition of the present invention, like the castrefractory composition, comprises refractory aggregates, a refractorypowder, an Al alloy powder and a dispersant. Also in this composition,an Al alloy powder is incorporated. Its purpose and effects arebasically the same as in the case of the cast refractory composition.

Further, with respect to the refractory aggregates, the refractorypowder and the dispersant, the same types as for the cast refractorycomposition, may be used.

In the spray refractory composition, the aluminum alloy powder may besomewhat different in the type and the amount from the aluminum alloypowder in the cast refractory composition. Namely, the aluminum alloypowder may comprise from 75 to 95 wt % of Al and from 5 to 25 wt % of Sior Mg, preferably from 80 to 93 wt % of Al and from 7 to 20 wt % of Sior Mg, and the purity is usually at least 90 wt % as the total of Al andSi or Mg.

Further, the alloy powder is used usually in an amount of from 0.05 to 5parts by weight, preferably from 0.1 to 3 parts by weight, per 100 partsby weight of the total amount of the refractory aggregates and therefractory powder.

The spray refractory composition of the present invention is adjusted byan addition of a prescribed amount of water to have self flowabilitysuitable for spraying.

For the spraying operation, the composition is transported through apiping to the application field and applied by spraying, and it isrequired to maintain the shape upon application.

Flowability desired for the spray refractory composition of the presentinvention may be defined as follows.

Namely, a batch immediately after mixing the spray refractorycomposition by an addition of a predetermined amount of water, is fed tofill a truncated cone mold having open upper and lower ends and havingan upper end inner diameter of 50 mm, a lower end inner diameter of 100mm and a height of 150 mm, and then the cone mold is withdrawn upward,whereupon the batch is left to stand still for 60 seconds, whereby theflowability is represented by the spread diameter (the mean value of thespread diameters measured in two directions, the unit being mm, whichwill be hereinafter referred to as a flow index).

Here, the measurement of the flow index of the batch is carried out in aroom of about 20° C. by mixing water of about 20° C. to the composition,and the measurement is completed within three minutes after mixing.

The batch exhibits self flowability when the flow index is at least 165mm. However, the flow index of the batch to be transported underpressure, is usually adjusted to a level of at least 190 mm, so that thebatch can easily and without retention be sent to the application fieldwhere a spray nozzle is located, by a force feed pump and a force feedpiping. By using a batch having a large flow index, the suctionresistance in the force feed pump and the flow resistance in the forcefeed piping can be made small, whereby the diameter of the force feedpiping can be made small, and the batch can be transported for a longdistance by force feeding. Accordingly, the flow index is preferably atleast 200 mm.

The above condition for the flow index is a preferred condition for thespray refractory composition. However, such a condition is sufficientlyadvantageous also for the cast refractory composition having selfflowability.

Likewise, the amount of water required to impart a desired flow index,may be the same as in the case of the cast refractory composition.

The spray refractory composition is transported to the application fieldusually in the form of a dried powder packaged in a bag, and at theapplication field, the composition and water are put into a mixer andmixed to obtain a batch, which is then applied by spraying by means ofe.g. the above-mentioned spray application installation. However, it isalso possible that the composition is mixed by an addition of waterbeforehand at a plant, and it is transported in the form of a mixedbatch by e.g. a concrete mixer car to the application field and thenspray application is carried out.

A rapid setting agent may be used to rapidly hard the spray refractorycomposition after its application. In such a case, it is preferred toinject the rapid setting agent to the flowable composition at the spraynozzle portion.

The rapid setting agent to be injected to the batch may be in the formof an aqueous solution of the rapid setting agent. However, in order toobtain a refractory having a low porosity by minimizing the amount ofwater in the batch to be applied by spraying, it is preferred to employa powdery rapid setting agent. The powdery rapid setting agent ispreferably injected to the batch from a rapid setting agent inlet usingcompressed air as a carrier so that the rapid setting agent will beuniformly dispersed in the batch. For the same reason, when the rapidsetting agent is injected to the batch in the form of an aqueoussolution, it is preferred to use an aqueous solution having aconcentration as high as possible.

As the rapid setting agent, it is possible to use an aluminate such assodium aluminate, potassium aluminate or calcium aluminate, a carbonatesuch as sodium carbonate, potassium carbonate, sodium hydrogen carbonateor potassium hydrogen carbonate, a sulfate such as sodium sulfate,potassium sulfate or magnesium sulfate, a calcium aluminate such as12CaO.7Al₂ O₃, 3CaO.Al₂ O₃ or 11CaO.7Al₂ O₃.CaF₂, calcium oxide, calciumhydroxide, or a composite or mixture thereof.

Among these rapid setting agents, it is preferred to use sodiumaluminate, since it is readily available and inexpensive, and its rapidsetting properties are stable. Sodium aluminate has a high meltingpoint, whereby refractoriness of the refractories will not bedeteriorated, and when injected into the batch, it undergoes hydrolysisto form a gel of Al(OH)₃ as well as NaOH, whereby the batch will berapidly hardened. Further, calcium aluminate preferred as the rapidsetting agent is the one wherein the CaO/Al₂ O₃ molar ratio is at least1.5.

The amount of the rapid setting agent to be injected, varies dependingupon the rapid setting agent to be used. However, it is usuallypreferably from 0.05 to 3 parts by weight per 100 parts by weight of thetotal amount of the refractory aggregates and the refractory powder inthe composition.

If the amount of the rapid setting agent injected, is less than 0.05part by weight, the setting speed tends to be inadequate, and theapplied batch is likely to flow off, even if a highly effective rapidsetting agent is employed. On the other hand, if it exceeds 3 parts byweight, hardening tends to be so rapid that the spray operation tends tobe difficult, and refractory properties such as heat resistance andcorrosion resistance tend to deteriorate. The amount of the rapidsetting agent to be injected is more preferably from 0.1 to 2 parts byweight. The rapid setting properties of the rapid setting agent varyalso depending upon its type. Accordingly, the amount is preferableadjusted to a proper level by selecting the type of the rapid settingagent or the length of the spray piping after injection of the rapidsetting agent.

The cast or spray refractory composition of the present inventioncontaining a predetermined amount of the Al--Si or Mg alloy powder per100 parts by weight of the total amount of the refractory aggregates andthe refractory powder in the composition, has good storage stability,since the activity of the Al--Si or Mg alloy powder is smaller than thatof Al powder, and with the batch having water mixed to this composition,the Al--Si or Mg alloy powder reacts with an aqueous alkaline solutionmore mildly than Al powder, and passages for discharging steam at thetime of drying the applied lining, are secured, whereby the appliedlining will not explode even when dried by rapidly raising thetemperature. It is thereby possible to obtain a refractory furnace wallwhich is dense and has excellent high temperature properties.

Accordingly, a long drying time required in the prior art will beunnecessary, and quick drying by direct flame may be employed, and theworking period can be substantially shortened. Further, the unit costcan be reduced, and the application operation and the environmentalsafety can be improved.

The batch for spraying of the present invention having self flowability,can be transported by a force feed pump, and the sprayed. Accordingly,the porosity of the applied lining can be substantially reduced ascompared with the porosity of the lining applied by the conventionalspray application method, whereby it is possible to obtain a lininghaving a bulk density comparable to the refractory applied by casting.As the rebound loss is little, the application yield is high. Further,dust scattered therearound, is remarkably little, and the workingenvironment is excellent.

Further, even when the spray application is carried out under a warm orhot condition, the resulting lining will not explode or peel and makes arefractory having a high bulk density and excellent corrosionresistance. Thus, it is suitable also as repairing refractories for e.g.a ladle, a tandish, or hot metal trough.

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that the presentinvention is by no means restricted to such specific Examples.

EXAMPLES 1 TO 22

Comparison of Cast Refractory Compositions of the Present Inventionusing an Aluminum-silicon Alloy Powder, Capable of being Rapidly Heatedand Dried, with Comparative Examples

Examples 1 to 7, 12 to 15 and 18 to 20 represent Examples of the presentinvention and Examples 8 to 11, 16 to 17 and 21 to 22 representComparative Examples.

As refractory aggregates, bauxite aggregates were used which had an Al₂O₃ content of 89 wt %, a SiO₂ content of 7 wt % and a Fe₂ O₃ content of1.3 wt % and which comprised coarse particles having a particle size offrom 1.68 to 5 mm, intermediate particles having a particle size of from0.1 to 1.68 and fine particles having a particle size of from 0.02 to0.1 mm and an average particle size of 0.03 mm.

As the refractory powder constituting the matrix of a refractory,aluminous cement having an average particles size of 9 μm and an Al₂ O₃content of 55 wt % and a CaO content of 36 wt %, Bayer alumina having apurity of Al₂ O₃ of 99.6 wt % and an average particle size of 4.3 μm,and fumed silica having purity of SiO₂ of 93 wt % and an averageparticles size of 0.8 μm, were employed. As the dispersant, a powder ofsodium tetraphosphate (Na₆ P₄ O₁₃) was employed which had a P₂ O₅content of 60.4 wt % and a Na₂ O content of 39.6 wt %.

As the Al--Si alloy powder, an alloy powder (a) comprising 80 wt % of anAl component and 20 wt % of a Si component, and an alloy powder (b)comprising 90 wt % of an Al component and 10 wt % of a Si component,were employed. The average particle sizes of the Al--Si alloy powders(a) and (b) were 28 μm and 30 μm, respectively, and they containedparticles having a particle size of at most 0.074 mm in an amount of 92%and 89%, respectively. Al powder used in Comparative Examples were theone having a purity of 99% and an average particle size of 30 μm.

Refractory aggregates, a refractory powder, a dispersant, an Al--Sialloy powder and an Al powder were weighed to obtain a cast refractorycomposition having the formulation (unit: parts by weight) as identifiedin Table 1, 2 or 3. Then, water was added thereto in the amount (partsby weight) as identified in Table 1, 2 or 3, per 100 parts by weight ofthe total amount of the refractory aggregates and the refractory powderin the composition, followed by mixing in a universal mixer for threeminutes to obtain a batch for cast refractories. This batch was castinto a formwork having an internal size of 40 mm×40 mm×160 mm and aformwork having an inner diameter of 100 mm and a height of 100 mm toobtain test specimens for cast refractories (Examples 1 to 11).

With respect to Examples 1 to 11 having self flowability, theflowability of each batch for cast refractories was determined in such amanner that a batch immediately after mixing is fed to fill a truncatedcone mold having open upper and lower ends and having an upper end innerdiameter of 50 mm, a lower end inner diameter of 100 mm and a height of150 mm, then the cone mold is withdrawn upward, and the batch is left tostand still for 60 seconds, whereupon spread diameters of the batch weremeasured in two directions by a caliper, and the average value was takenas the batch flow index.

The apparent porosity and the bulk density were measured in accordancewith the methods stipulated in JIS R2205 after drying each test specimenat 110° C. for 24 hours.

The flexural strength was measured with respect to a test specimenhaving a size of 40 mm×40 mm×160 mm which was cured at room temperatureand a test specimen having the same size which was dried and then firedat 1,400° C. for one hour.

The dimensional change was determined in such a manner that thedimensional change in a test specimen which was fired at 1,400° C. forone hour was measured, and represented by the ratio based on the sizebefore firing. "Bulge" shown in a Table means that a distinct bulge of afew % was observed.

The presence or absence of cracking represents the result of examinationof the outer appearance of a test specimen removed from the forms afterhardening.

The explosion resistance was evaluated in such a manner that a testspecimen having a diameter of 100 mm and a height of 100 mm taken outfrom the forms was put into an electric furnace maintained at 1,200° C.,whereupon the presence or absence of explosion was examined.

Examples 12 to 17 represent test results of cast refractories whereinaluminous cement as a refractory powder was incorporated excessively,and no other refractory powder was incorporated, whereby selfflowability was not sufficient. The batch flow index of castrefractories in each of Examples 12 to 17 (as well as Examples 18 to 22)was determined in such a manner that using a flow cone stipulated in JISR5201, the batch immediately after mixing was fed to fill the flow conemounted on a vibrating table, then a vibration of 3G was exertedthereto, and upon expiration of 10 seconds, spread diameters of thebatch were measured in two directions by a caliper, and the mean valuewas taken as the flow index. The evaluation methods for other items withrespect to Examples 12 to 17 were the same as in Examples 1 to 11.

Examples 18 to 22 represent test results of cast refractories in whichrefractory clay was incorporated. The refractory aggregates, therefractory powder and other materials used were the same as in Examples1 to 11, and the evaluation methods were the same as in Example 12.

It is evident from Tables 1, 2 and 3, when cast refractory compositionscontaining an Al--Si alloy powder of the present invention are employed,gas permeable pores for discharging steam are secured even if theapplied refractories are dense, and bulging or cracking will not formwhich is likely to result due to generation of H₂ gas in the case ofcasting refractories containing Al powder, and no explosion takes placeeven when the applied refractories are dried under a rapidly heatingcondition. The physical properties of the applied cast refractories areexcellent since they are dense. Whereas, cast refractories containing Alpowder have problems such that when the content of Al powder is large,bulging or cracking occurs, and the preferred content of Al powdervaries depending upon the mixing temperature of the batch.

                                      TABLE 1                                     __________________________________________________________________________    Examples    1   2   3   4   5   6   7   8                                     __________________________________________________________________________    Bauxite coarse particles                                                                  31  31  31  31  31  31  31  31                                    Bauxite intermediate                                                                      25  25  25  25  25  25  25  25                                    particles                                                                     Bauxite fine particles                                                                    23  23  23  23  23  23  23  23                                    Aluminous cement                                                                          8   8   8   8   8   8   8   8                                     Bayer alumina                                                                             7   7   7   7   7   7   7   7                                     Fumed silica                                                                              6   6   6   6   6   6   6   6                                     90Al-10Si alloy powder                                                                    0.05                                                                              0.1 0.5 1   2   --  --  --                                    80Al-20Si alloy powder                                                                    --  --  --  --  --  0.5 1   0.03                                  Al powder   --  --  --  --  --  --  --  --                                    Dispersant  0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1                                   Water content                                                                             8   8   8   8   8   8   8   8                                     Batch flow index (mm)                                                                     >245                                                                              >245                                                                              >245                                                                              >245                                                                              >245                                                                              >245                                                                              >245                                                                              >245                                  Apparent porosity (%)                                                                     12.1                                                                              12.0                                                                              12.5                                                                              12.6                                                                              13.0                                                                              12.3                                                                              12.7                                                                              11.8                                  Bulk density (g/cc)                                                                       2.85                                                                              2.85                                                                              2.83                                                                              2.83                                                                              2.84                                                                              2.84                                                                              2.82                                                                              2.85                                  Flexural strength (kg/cm.sup.2)                                               After curing                                                                              120 118 123 125 115 115 118 120                                   After 1,400° C. × 1 hr                                                       400 400 412 400 398 398 400 405                                   Dimensional change (%)                                                                    0.03                                                                              0.05                                                                              0.05                                                                              0.07                                                                              0.07                                                                              0.03                                                                              0.05                                                                              0.03                                  Cracking    Nil Nil Nil Nil Nil Nil Nil Nil                                   Explosion   Nil Nil Nil Nil Nil Nil Nil Present                               __________________________________________________________________________

                                      TABLE 2                                     __________________________________________________________________________    Examples   9   10  11  12  13  14  15  16                                     __________________________________________________________________________    Bauxite coarse particles                                                                 31  31  31  35  35  35  35  35                                     Bauxite intermediate                                                                     25  25  25  27  27  27  27  27                                     particles                                                                     Bauxite fine particles                                                                   23  23  23  25  25  25  25  25                                     Aluminous cement                                                                         8   8   8   13  13  13  13  -13                                    Bayer alumina                                                                            7   7   7   --  --  --  --  --                                     Fumed silica                                                                             6   6   6   --  --  --  --  --                                     90Al-10Si alloy powder                                                                   3.5 --  --  0.1 0.5 1   2   --                                     80Al-20Si alloy powder                                                                   --  --  --  --  --  --  --  --                                     Al powder  --  1   --  --  --  --  --  --                                     Dispersant 0.1 0.1 0.1 --  --  --  --  --                                     Water content                                                                            8   8   8   6   6   6   6   6                                      Batch flow index (mm)                                                                    >245                                                                              >245                                                                              >245                                                                              >220                                                                              >220                                                                              >220                                                                              >220                                                                              >220                                   Apparent porosity (%)                                                                    13.4                                                                              15.4                                                                              12.0                                                                              14.5                                                                              14.8                                                                              15.0                                                                              15.2                                                                              14.9                                   Bulk density (g/cc)                                                                      2.75                                                                              2.68                                                                              2.85                                                                              2.76                                                                              2.74                                                                              2.78                                                                              2.76                                                                              2.75                                   Flexural strength                                                             (kg/cm.sup.2)                                                                 After curing                                                                             105 85  120 110 105 103 100 100                                    After 1,400° C. × 1 hr                                                      320 200 410 410 420 416 415 430                                    Dimensional change (%)                                                                   Bulge                                                                             Bulge                                                                             0.03                                                                              0.01                                                                              0.02                                                                              0.04                                                                              0.05                                                                              -0.01                                  Cracking   Present                                                                           Present                                                                           Nil Nil Nil Nil Nil Nil                                    Explosion  Nil Nil Present                                                                           Nil Nil Nil Nil Present                                __________________________________________________________________________

                  TABLE 3                                                         ______________________________________                                        Examples    17      18     19   20   21    22                                 ______________________________________                                        Bauxite coarse                                                                            35      35     35   35   35    35                                 particles                                                                     Bauxite intermediate                                                                      27      30     30   30   30    30                                 particles                                                                     Bauxite fine particles                                                                    25      25     25   25   25    25                                 Aluminous cement                                                                          13      1      1    1    1     1                                  Refractory clay                                                                           --      5      5    5    5     5                                  Bayer alumina                                                                             --      3      3    3    3     3                                  Fumed silica                                                                              --      1      1    1    1     1                                  80Al-20Si alloy                                                                           --      0.1    0.5  1    --    --                                 powder                                                                        Al powder   1       --     --   --   --    0.5                                Dispersant  --      0.1    0.1  0.1  0.1   0.1                                Water content                                                                             6       5      5    5    5     5                                  Batch flow index                                                                          >220    >220   >220 >220 >220  >220                               (mm)                                                                          Apparent porosity                                                                         17.4    16.0   16.2 16.4 16.5  18.8                               (%)                                                                           Bulk density                                                                              2.54    2.75   2.74 2.70 2.74  2.56                               (g/cc)                                                                        Flexural strength                                                             (kg/cm.sup.2)                                                                 After curing                                                                              80      25     24   27   25    18                                 After 1,400° C. × 1 hr                                                       210     415    420  420  430   350                                Dimensional change                                                                        Bulge   0.02   0.04 0.03 -0.02 Bulge                              (%)                                                                           Cracking    Present Nil    Nil  Nil  Nil   Present                            Explosion   Nil     Nil    Nil  Nil  Present                                                                             Nil                                ______________________________________                                    

EXAMPLES 23 TO 44

Comparison of Cast Refractory Compositions employing anAluminum-magnesium Alloy Powder, Capable of being Rapidly Heated forDrying, with Comparative Examples

Examples 23 to 30, 32 to 37 and 40 42 represent Examples of the presentinvention, and Examples 30 to 33, 38 to 39 and 43 to 44 representComparative Examples. (Comparative Examples 32, 33, 43 and 44 are thesame as previous Comparative Examples 10, 11, 21 and 22, respectively.)

As refractory aggregates, bauxite aggregates which had an Al₂ O₃ contentof 89 wt %, a SiO₂ content of 7 wt % and a Fe₂ O₃ content of 1.3 wt %and which comprised coarse particles having a particle size of from 1.68to 5 mm, intermediate particles having a particle size of from 0.1 to1.68 mm, and fine particles having a particle size of from 0.02 to 0.1mm and an average particle size of 0.03 mm, and spinel aggregates whichhad an Al₂ O₃ content of 73 wt % and a MgO content of 26 wt % and whichcomprised intermediate particles having a particle size of from 0.1 to1.68 mm, and fine particles having a particle size of from 0.02 to 0.1mm and an average particle size of 0.05 mm, were used.

As the refractory powder constituting the matrix of the refractories,the same aluminous cement, Bayer alumina and fumed silica as used inforegoing Examples 1 to 22, were used.

The dispersant used was the same as used in the previous Examples.

As an Al--Mg alloy powder, an alloy powder (a) comprising 80 wt % of anAl component and 20 wt % of a Mg component, and an alloy powder (b)comprising 90 wt % of an Al component and 10 wt % of a Mg component,were employed. The average particle sizes of the Al--Mg alloy powders(a) and (b) were 28 μm and 30 μm, respectively, and they containedparticles having a particle size of at most 0.074 mm in an amount of 92%and 89%, respectively. The Al powder used in Comparative Examples wasthe one having a purity of 99%, and an average particle size of 30 μm.

Using the compositions as identified in Tables 4, 5 and 6, testspecimens were prepared in the same manner as in the previous Examples.The flow index, the apparent porosity, the bulk density, the flexuralstrength, the dimensional change, the presence or absence of crackingand the presence or absence of explosion were measured by the samemethods as in the previous Examples.

It is evident from Tables 4, 5 and 6 that when cast refractorycompositions containing an Al--Mg alloy powder of the present inventionare used, substantially the same results as in the case where an Al--Sialloy powder was used, are obtainable i.e. gas permeable pores fordischarging steam during drying are secured even if the appliedrefractories are dense, and bulging or cracking will not form which islikely to form due to generation of H₂ gas in the case of castrefractories containing Al powder, and no explosion will occur even whenthe applied refractories are dried under a rapidly heating condition.The physical properties of the applied test refractories were excellent,since they were dense.

                                      TABLE 4                                     __________________________________________________________________________    Examples    23  24  25  26  27  28  29  30                                    __________________________________________________________________________    Bauxite coarse particles                                                                  31  31  31  31  31  31  31  31                                    Bauxite intermediate                                                                      25  25  25  25  25  25  25  25                                    particles                                                                     Bauxite fine particles                                                                    23  23  23  23  23  23  23  23                                    Aluminous cement                                                                          8   8   8   8   8   8   8   8                                     Bayer alumina                                                                             7   7   7   7   7   7   7   7                                     Fumed silica                                                                              6   6   6   6   6   6   6   6                                     90Al-10 Mg alloy powder                                                                   0.05                                                                              0.1 0.5 1   2   --  --                                        80Al-20 Mg alloy powder                                                                   --  --  --  --  --  0.5 1   0.03                                  Dispersant  0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1                                   Water content                                                                             8   8   8   8   8   8   8   8                                     Batch flow index (mm)                                                                     >245                                                                              >245                                                                              >245                                                                              >245                                                                              >245                                                                              >245                                                                              >245                                                                              >245                                  Apparent porosity (%)                                                                     12.1                                                                              12.3                                                                              12.5                                                                              12.8                                                                              13.5                                                                              12.4                                                                              12.9                                                                              11.5                                  Bulk density (g/cc)                                                                       2.85                                                                              2.84                                                                              2.83                                                                              2.82                                                                              2.78                                                                              2.83                                                                              2.81                                                                              2.84                                  Flexural strength (kg/cm.sup.2)                                               After curing                                                                              121 115 123 120 115 113 117 120                                   After 1,400° C. × 1 hr                                                       400 400 410 410 405 400 405 400                                   Dimensional change (%)                                                                    0.03                                                                              0.04                                                                              0.05                                                                              0.07                                                                              0.08                                                                              0.03                                                                              0.04                                                                              0.03                                  Cracking    Nil Nil Nil Nil Nil Nil Nil Nil                                   Explosion   Nil Nil Nil Nil Nil Nil Nil Present                               __________________________________________________________________________

                                      TABLE 5                                     __________________________________________________________________________    Examples    31  32  33  34  35  36  37  38                                    __________________________________________________________________________    Bauxite coarse particles                                                                  31  31  31  40  40  40  40  40                                    Bauxite intermediate                                                                      25  25  25  6   6   6   6   6                                     particles                                                                     Bauxite fine particles                                                                    23  23  23  15  15  15  15  15                                    Spinel intermediate                                                                       --  --  --  20  20  20  20  20                                    particles                                                                     Spinel fine particles                                                                     --  --  --  6   6   6   6   6                                     Aluminous cement                                                                          8   8   8   13  13  13  13  13                                    Bayer alumina                                                                             7   7   7   --  --  --  --  --                                    Fumed silica                                                                              6   6   6   --  --  --  --  --                                    90Al-10 Mg alloy powder                                                                   3.5 --  --  0.1 0.5 1   2   --                                    Al powder   --  1   --  --  --  --  --  --                                    Dispersant  0.1 0.1 0.1 --  --  --  --  --                                    Water content                                                                             8   8   8   6   6   6   6   6                                     Batch flow index (mm)                                                                     >245                                                                              >245                                                                              >245                                                                              >215                                                                              >215                                                                              >215                                                                              >215                                                                              >215                                  Apparent porosity (%)                                                                     13.8                                                                              15.4                                                                              12.0                                                                              14.5                                                                              14.9                                                                              15.0                                                                              15.3                                                                              14.9                                  Bulk density (g/cc)                                                                       2.74                                                                              2.68                                                                              2.85                                                                              2.75                                                                              2.75                                                                              2.74                                                                              2.73                                                                              2.75                                  Flexural strength (kg/cm.sup.2)                                               After curing                                                                              100 85  120 110 105 103 98  100                                   After 1,400° C. × 1 hr                                                       315 200 410 415 420 410 405 430                                   Dimensional change (%)                                                                    Bulge                                                                             Bulge                                                                             0.03                                                                              0.01                                                                              0.02                                                                              0.04                                                                              0.05                                                                              -0.01                                 Cracking    Present                                                                           Present                                                                           Nil Nil Nil Nil Nil Nil                                   Explosion   Nil Nil Present                                                                           Nil Nil Nil Nil Present                               __________________________________________________________________________

                  TABLE 6                                                         ______________________________________                                        Examples    39      40     41   42   43    44                                 ______________________________________                                        Bauxite coarse                                                                            40      35     35   35   35    35                                 particles                                                                     Bauxite intermediate                                                                      6       30     30   30   30    30                                 particles                                                                     Bauxite fine particles                                                                    15      25     25   25   25    25                                 Spinel intermediate                                                                       20      --     --   --   --    --                                 particles                                                                     Spinel fine particles                                                                     6       --     --   --   --    --                                 Aluminous cement                                                                          13      1      1    1    1     1                                  Refractory clay                                                                           --      5      5    5    5     5                                  Bayer alumina                                                                             --      3      3    3    3     3                                  Fumed silica                                                                              --      1      1    1    1     1                                  80Al-20Mg alloy                                                                           --      0.1    0.5  1    --    --                                 powder                                                                        Al powder   1       --     --   --   --    0.5                                Dispersant  --      0.1    0.1  0.1  0.1   0.1                                Water content                                                                             6       5      5    5    5     5                                  Batch flow index                                                                          >215    >205   >205 >205 >205  >205                               (mm)                                                                          Apparent porosity (%)                                                                     17.4    16.1   16.2 16.7 16.5  18.8                               Bulk density (g/cc)                                                                       2.54    2.76   2.75 2.72 2.74  2.56                               Flexural strength                                                             (kg/cm.sup.2)                                                                 After curing                                                                              80      25     28   24   25    18                                 After 1,400° C. × 1 hr                                                       210     410    420  425  430   350                                Dimensional change                                                                        Bulge   0.02   0.03 0.04 -0.02 Bulge                              (%)                                                                           Cracking    Present Nil    Nil  Nil  Nil   Present                            Explosion   Nil     Nil    Nil  Nil  Present                                                                             Nil                                ______________________________________                                    

In the following Examples, some of the compositions of the previousExamples were used for application to the inner surface of a furnace,followed by rapid heating for drying. However, the method for forming afurnace wall of the present invention is by no means restricted by suchspecific Examples.

EXAMPLES 45 AND 46

The compositions of Examples 3 and 24 were, respectively, applied tominitandish furnaces. Each composition was applied in a thickness of 250mm over an area of 1,000×1,000 mm on the inner surface of a heatinsulating castable refractory formed in a thickness of 100 mm on therear side. After curing the applied monolithic refractory, the surfaceof the applied refractory was heated by an oil burner. The heating fordrying was carried out in each case at a heating up rate of 200° C./hrat the surface until the surface temperature became 1,000° C.

The temperature distribution in the minitandish furnace was ±20° C.

In each case, no explosion occurred during the drying operation, andupon completion of the drying, no crack was observed on the surface ofthe furnace wall thus formed.

The furnace wall was cut out, and the cross section in the thicknessdirection was inspected, whereby no crack was observed.

EXAMPLES 47 AND 48

The monolithic refractory compositions of Examples 7 and 28 were,respectively, applied to minitandish furnaces, and drying tests werecarried out, in the same manner as in Examples 45 and 46. In this case,the surface temperature of the furnace wall was raised at a heating uprate of 300° C./hr to 1,400° C. for drying. In each case, no explosionoccurred during the drying operation, and after completion of thedrying, no crack was observed on the surface or the cross section of thefurnace wall.

EXAMPLES 49 AND 50

The monolithic refractory compositions of Examples 18 and 41 were,respectively, applied, while exerting a vibration, to minitandishfurnaces, and drying tests were carried out, in the same manner as inExamples 45 and 46. In this case, the surface temperature of the furnacewall was raised at a heating up rate of 100° C./hr to 1,000° C. fordrying. In each case, no explosion occurred during the drying operation,and after the drying, no crack was observed.

COMPARATIVE EXAMPLES 51 AND 52

The monolithic refractory compositions of Comparative Examples 11 and 33were, respectively, applied to minitandish furnaces, and drying testswere carried out in the same manner as in Examples 45 and 46. Thesurface temperature of the furnace wall was raised at a heating up rateof 200° C./hr to 1,200° C. for drying. In each case, explosion occurredduring the drying operation, and a part of the furnace wall surface blewoff. After completion of the drying, many cracks were observed on thefurnace wall.

COMPARATIVE EXAMPLES 53 AND 54

The monolithic refractory compositions of Examples 14 and 36 were,respectively, applied, while exerting a vibration, to minitandishfurnaces in the same manner as in Examples 45 and 46, and the surfacetemperature of each furnace wall was raised at a heating up rate of 500°C./hr to 1,000° C. for drying.

In each case, no explosion was observed during the drying, but aftercompletion of the drying, a numerous cracks which appeared to bespalling, were observed on the surface of the surface wall.

From the foregoing results, an interrelation is observed as between thedrying tests by minitandish furnaces and tests on explosion with thecompositions, and it has been found that evaluation of the compositionsmay be applicable to the evaluation of the process for forming a furnacewall under rapid heating condition.

EXAMPLES 55 TO 67

Comparison of Spray Refractory Compositions employing an AluminumSilicon or Magnesium Alloy Powder, Capable of being Rapidly Heated forDrying, with Comparative Examples

Examples 55 to 61 and 63 represent Examples of the present invention,and Examples 62 and 64 to 67 represent Comparative Examples. Therefractory aggregates, the refractory powder, the aluminum powder andthe dispersant were the same as used in Examples 1 to 22. As the Alalloy powder, the one having an Al content of 88 wt % and a Si contentof 12 wt % (Al alloy powder (a)) and the one having a Al content of 85wt % and a Mg content of 15 wt % (Al alloy powder (b)) were used.

The average particle sizes of the Al alloy powders (a) and (b) wereabout 30 μm and about 35 μm, respectively, and they contained particleshaving a particle size of at most 0.074 mm in an amount of 90 wt % and88 wt %, respectively.

As the rapid setting agent, the one which is a powder having an averageparticles size of about 150 μm and which is a mixture comprising sodiumaluminate (containing water of crystallization of about 20%) and sodiumcarbonate in a weight ratio of 3:1, was used.

In a room of 20° C., the refractory aggregates, the refractory powder,the Al alloy powder and the dispersant were blended to prepare therespective compositions as identified in Tables 7 and 8. Water of about20° C. was added to each composition in the amount as identified inTable 7 or 8 (in Tables 7 and 8, the refractory aggregates and therefractory powder are shown by wt %, and others are shown by parts byweight per 100 parts by weight of the total amount of the refractoryaggregates and the refractory powder), followed by mixing in a mixerhaving a capacity of 500 kg for 3 minutes to obtain a batch. The flowindex of each batch was measured by the same measuring method as inExamples 1 to 11.

Each batch thus prepared was applied by spraying to a substantiallyvertical wall surface in a thickness of about 100 mm.

The application by spraying was carried out in such a manner that thebatch was transported by a force feed pump through a force feed piping,and the rapid setting agent was injected and mixed thereto at a portionbefore a spray nozzle, whereupon the mixed batch was sprayed from thespray nozzle.

The spray application method of the present invention was a wet system,whereby a rebound loss and formation of a dust during the sprayapplication were very small as compared with a dry or semi-dry sprayapplication method, whereby the application yield was high, and theworking environment was remarkably good.

Then, a test specimen having a size of about 300 mm×300 mm×100 mm wastaken from each lining formed by spraying in a thickness of about 100 mmon the wall surface. This test specimen was dried at 110° C. for 24hours, whereupon the specimen was visually inspected to see the presenceor absence of cracking, and then the porosity and the bulk density weremeasured in accordance with the methods stipulated in JIS R2205.

Further, a test specimen having a diameter of 100 mm and a height of 100mm was taken from each lining, and the explosion was evaluated withrespect to each test specimen. Namely, each test specimen was put intoan electric furnace maintained at 1,200° C., and after taking it out,the presence or absence of explosion was examined and evaluated.

The flexural strength was measured with respect to a test specimenhaving a size of 40 mm×40 mm×150 mm taken from each lining, which wasdried at 110° C. for 24 hours, and a test specimen having the same size,which was fired at 1,400° C. for 3 hours. The dimensional change wasdetermined in such a manner that the dimensional change as betweenbefore and after firing was measured with respect to the test specimenfor flexural strength fired at 1,400° C. for 3 hours, and the resultsare shown in Tables 9 and 10. "Bulge" shown for the dimensional changein Tables 9 and 10 means that a distinct bulge of a few % was observed.

Each of the spray refractories of Examples 56 to 59 and 61 andComparative Examples 62 and 64 to 67, was applied by spraying to afurnace wall (temperature: about 500° C.) assumed to be a slag lineportion of a ladle which wore out and required repair, whereby theadhesion to the wall surface to be repaired and the presence or absenceof explosion and falling off were examined. The results are shown inTables 9 and 10.

Examples 64 and 65 represent cases wherein the amount of the rapidsetting agent injected was not suitable. In Example 64, the rapidsetting agent was inadequate, whereby the batch flowed off from the wallsurface, and a satisfactory lining was not obtained. In Example 65, therapid setting agent was excessive, whereby curing of the batch proceededrapidly, and the spray application was unstable, and the adhesion to thewall surface was poor, whereby a rebound loss was substantial, and asatisfactory lining was not obtained. Therefore, no measurement of thephysical properties could be done with respect to the lining of Example65.

Example 66 represents a case where Al powder was incorporated, wherebythe spray application was carried out without any trouble, but bulgingof the lining occurred, and the lining became porous, and cracks werealso observed.

It is evident that the physical properties of the linings formed byspray application by the present invention are comparable to thephysical properties of linings formed by casting.

Further, a hot spray application test was carried out to simulate repairof a wall surface of a ladle of 500° C., which wore out, whereby withthe compositions of Examples 56 to 59, 61 and 63, good adhesion wasobserved, and no cracking or falling off due to explosion was observed.Further, with the compositions of Examples 62 and 64 to 67, the adhesionwas poor, or cracking or falling off due to explosion was observed.

As shown in Tables 9 and 10, when the spray refractories containing anAl alloy powder of the present invention are applied by spraying, denselinings equivalent to the cast refractories can be obtained, and even ifthe linings are dense, gas permeable pores discharging steam are securedin the linings, whereby even when the linings are dried under a rapidheating temperature condition, no explosion occurs. Further, therefractory properties such as corrosion resistance of the linings areexcellent, since the linings are dense with a small porosity.

                  TABLE 7                                                         ______________________________________                                        Examples    55     56     57   58   59   60   61                              ______________________________________                                        Refractory aggregates                                                         Bauxite coarse                                                                            31     31     31   31   31   31   31                              particles                                                                     Bauxite intermediate                                                                      25     25     25   25   25   25   25                              particles                                                                     Bauxite fine particles                                                                    23     23     23   23   23   23   23                              Refractory powder                                                             Aluminous cement                                                                          8      8      8    8    8    8    8                               Bayer alumina                                                                             7      7      7    7    7    7    7                               Fumed silica                                                                              6      6      6    6    6    6    6                               88Al-12Si alloy                                                                           0.05   0.1    0.5  1    2    --   --                              powder (a)                                                                    85Al-15Mg alloy                                                                           --     --     --   --   --   0.5  1                               powder (b)                                                                    Al powder   --     --     --   --   --   --   --                              Dispersant  0.01   0.1    0.1  0.1  0.1  0.1  0.1                             Rapid setting agent                                                                       0.5    0.5    0.5  0.5  0.5  0.5  0.5                             Water content                                                                             8      8      8    9    9    8    9                               ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                        Examples       62     63     64   65   66   67                                ______________________________________                                        Refractory aggregates                                                         Bauxite coarse 31     31     31   31   31   31                                particles                                                                     Bauxite intermediate                                                                         25     25     25   25   25   25                                particles                                                                     Bauxite fine particles                                                                       23     23     23   23   23   23                                Refractory powder                                                             Aluminous cement                                                                             8      8      8    8    8    8                                 Bayer alumina  7      7      7    7    7    7                                 Fumed silica   6      6      6    6    6    6                                 88Al-12Si alloy powder (a)                                                                   0.03   0.05   1    --   --   --                                85Al-15Mg alloy powder (b)                                                                   --     --     --   1    --   --                                Al powder      --     --     --   --   1    --                                Dispersant     0.01   0.1    0.1  0.1  0.1  0.1                               Rapid setting agent                                                                          0.5    0.5    0.03 5    0.5  0.5                               Water content  8      9      9    9    9    8                                 ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                        Examples    55     56     57   58   59   60   61                              ______________________________________                                        Flow index (mm)                                                                           >250   >250   >250 >250 >250 >250 >250                            Force feeding property                                                                    Good   Good   Good Good Good Good Good                            Adhesion to wall                                                                          Good   Good   Good Good Good Good Good                            surface                                                                       Flow off of batch after                                                                   Nil    Nil    Nil  Nil  Nil  Nil  Nil                             application                                                                   Apparent porosity (%)                                                                     12.4   12.5   12.7 12.9 13.2 12.6 12.8                            Bulk density (g/cc)                                                                       2.84   2.84   2.83 2.82 2.80 28.5 2.81                            Flexural strength                                                             (kg/cm.sup.2)                                                                 After 1,100° C. ×                                                            121    125    123  121  118  120  119                             24 hr                                                                         After 1,400° C. ×                                                            400    402    400  395  390  405  398                             3 hr                                                                          Dimensional change                                                                        0.01   0.01   0.03 0.05 0.06 0.01 0.05                            (%)                                                                           Cracking    Nil    Nil    Nil  Nil  Nil  Nil  Nil                             Explosion   Nil    Nil    Nil  Nil  Nil  Nil  Nil                             Adhesion to wall of                                                                       --     Good   Good Good Good --   Good                            500° C.                                                                Explosion or cracking                                                                     --     Nil    Nil  Nil  Nil  --   Nil                             Falling off --     Nil    Nil  Nil  Nil  --   Nil                             ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                        Examples   62      63     64    65   66    67                                 ______________________________________                                        Flow index (mm)                                                                          >250    >250   >250  >250 >250  >250                               Force feeding                                                                            Good    Good   Good  Good Good  Good                               property                                                                      Adhesion to wall                                                                         Good    Good   Poor  Poor Good  Good                               surface                                                                       Flow off of batch                                                                        Nil     Nil    Present                                                                             --   Nil   Nil                                after application                                                             Apparent porosity                                                                        12.4    13.9   --    --   15.0  12.5                               (%)                                                                           Bulk density (g/cc)                                                                      2.85    2.72   --    --   2.67  2.85                               Flexural strength                                                             (kg/cm.sup.2)                                                                 After 1,100° C. ×                                                           120     96     --    --   75    120                                24 hr                                                                         After 1,400° C. ×                                                           400     295    --    --   200   400                                3 hr                                                                          Dimensional change                                                                       0.01    0.15   --    --   Bulge 0.01                               (%)                                                                           Cracking   Nil     Nil    --    --   Present                                                                             Nil                                Explosion  Present Nil    --    --   Nil   Present                            Adhesion to wall                                                                         Good    Good   Fair  Poor Good  Good                               of 500° C.                                                             Explosion or                                                                             Nil     Nil    Nil   --   Nil   Present                            cracking                                                                      Falling off                                                                              Present Nil    Present                                                                             --   Nil   Present                            ______________________________________                                    

EXAMPLE 68

The monolithic refractory composition of Example 56 was applied byspraying to a furnace wall of a minitandish furnace. The composition wasapplied by spraying in a thickness of 250 mm over an area of 1,000×1,000mm on the inner surface of a heat insulting castable refractory formedin a thickness of 100 mm on the rear side. After curing the appliedmonolithic refractory, the applied refractory surface was heated by anoil burner.

The heating for drying was carried out so that the surface temperaturewas raised at a heating up rate of 200° C./hr to 1,000° C. Thetemperature distribution in the minitandish furnace was about ±20° C.

No explosion was observed during the drying operation, and aftercompletion of the drying, no crack was observed on the surface of thefurnace wall formed. Further, the furnace wall was cut out, and thecross section in the thickness direction was inspected, whereby no crackwas observed.

EXAMPLE 69

The monolithic refractory composition of Example 58 was applied to theminitandish furnace, and the drying test were carried out, in the samemanner as in Example 68. In this case, the surface temperature of thefurnace wall was raised at a heating up rate of 300° C./hr to 1,400° C.for drying. No explosion was observed during the drying operation, andafter completion of the drying, no crack was observed on the surface orthe cross section of the furnace wall.

EXAMPLE 70

The monolithic refractory composition of Example 60 was applied to aminitandish furnace, and the drying test was carried out, in the samemanner as in Example 68. In this case, the surface temperature of thefurnace wall was raised at a heating up rate of 100° C./hr to 1,000° C.for drying. No explosion was observed during the drying operation, andafter the drying, no crack was observed.

COMPARATIVE EXAMPLE 71

The monolithic refractory composition of Comparative Example 62 wasapplied to a minitandish furnace, and the drying test was carried out,in the same manner as in Example 68. The surface temperature of thefurnace wall was raised at a heating up rate of 200° C./hr to 1,200° C.for drying. During the drying, explosion occurred, and a part of thefurnace wall surface blew off. After completion of the drying, manycracks were observed on the furnace wall.

COMPARATIVE EXAMPLE 7

The monolithic refractory composition of Example 61 was applied to aminitandish furnace in the same manner as in Example 68, and the surfacetemperature of the furnace wall was raised at a heating up rate of 500°C./hr to 1,000° C. for drying.

During the drying operation, no explosion was observed, but aftercompletion of the drying, a numerous cracks which appeared to bespalling were observed on the surface of the furnace wall.

From the foregoing results, an interrelation is observed as between thedrying test by a minitandish furnace and the test on explosion with thecomposition, and it has been found that evaluation of the composition isapplicable also to the evaluation of the process of forming a furnacewall under a rapid heating condition.

What is claimed is:
 1. A process for forming a furnace wall, whichcomprises applying to a predetermined furnace wall-forming portion bycasting or spraying, a monolithic refractory batch prepared by mixing apredetermined amount of water to a composition comprising refractoryaggregates, a refractory powder, a dispersant and an aluminum alloypowder, wherein the aluminum alloy powder is contained in an amount offrom 0.04 to 5 parts by weight per 100 parts by weight of a total amountof the refractory aggregates and the refractory powder, to form arefractory of the furnace wall, then carrying out a heat treatment byheating the refractory thus applied at a heating up rate of from 50 to400° C./hr at a surface of the refractory, wherein the heat treatment iscarried out at least until a temperature of the surface of therefractory becomes at least 500° C., to dry the refractory.
 2. Theprocess according to claim 1, wherein the aluminum alloy powdercomprises from 60 to 95 wt % of Al and from 5 to 40 wt % of Si or Mg. 3.The process according to claim 1, wherein the aluminum alloy powdercomprises from 85 to 93 wt % of Al and from 7 to 15 wt % of Si.
 4. Theprocess according to claim 1, wherein the aluminum alloy powdercomprises at least 90 wt % of Al and Si or Mg and contains at least 40wt % of particles having a particle size of at most 0.074 mm.
 5. Theprocess according to claim 1, wherein the refractory powder containsaluminous cement.
 6. The process according to claim 1, wherein therefractory applied by casting or spraying is heated and dried at aheating up rate of 100° C./hr to 400° C./hr.
 7. The process according toclaim 1, wherein the refractory applied by casting or spraying is heatedand dried until the surface temperature becomes 1000° C.
 8. A processfor forming a furnace wall, which comprises applying, to a predeterminedfurnace wall-forming portion by casting, a monolithic refractory batchprepared by mixing a predetermined amount of water to a compositioncomprising refractory aggregates, a refractory powder, a dispersant andan aluminum alloy powder, wherein the aluminum alloy powder is containedin an amount of from 0.04 to 3 parts by weight per 100 parts by weightof a total amount of the refractory aggregates and the refractorypowder, to form a refractory of the furnace wall, then carrying out aheat treatment by heating the refractory thus applied, at a heating uprate of from 50 to 400° C./hr at a surface of the refractory, whereinthe heat treatment is carried out at least until a temperature of thesurface of the refractory becomes at least 500° C., to dry therefractory.
 9. The process according to claim 8, wherein the aluminumalloy powder in the composition is in an amount of from 0.1 to 1 part byweight per 100 parts by weight of the total amount of the refractoryaggregates and the refractory powder.
 10. A process for forming afurnace wall, which comprises applying to a predetermined furnacewall-forming portion by spraying, a monolithic refractory batch preparedby mixing a predetermined amount of water to a composition comprisingrefractory aggregates, a refractory powder, a dispersant and an aluminumalloy powder, wherein the aluminum alloy powder is contained in anamount of from 0.05 to 5 parts by weight per 100 parts by weight of atotal amount of the refractory aggregates and the refractory powder, toform a refractory of the furnace wall, then carrying out a heattreatment by heating the refractory thus applied, at a heating up rateof from 50 to 400° C./hr at a surface of the refractory, wherein theheat treatment is carried out at least until a temperature of thesurface of the refractory becomes at least 500° C., to dry therefractory.
 11. The process according to claim 10, wherein the aluminumalloy powder in the composition is in an amount of from 0.1 to 3 partsby weight per 100 parts by weight of the total amount of the refractoryaggregates and the refractory powder.